Light absorbed by a semiconductor is stored as electronic excitations in the form of bound electron-hole pairs, also known as excitons. There is a rich variety of semiconductor nanostructures available today for the design of novel material systems and interfaces with tailor-made functionalities. In particular, atomically thin two-dimensional (2D) materials such as graphene and transition metal dichalcogenide (TMDC) monolayers exhibit extraordinary optical and electrical properties. For such materials, with thicknesses below 1 nanometer, I will show that the external dielectric environment strongly influences their intrinsic electronic states , energy transfer processes , and excited-state dynamics . I will also briefly discuss new experimental approaches to the study of these phenomena and the associated ultrafast dynamics. In addition to the intrinsic scientific interest in understanding materials in this distinctive regime, such control offers a non-invasive approach to engineer material properties and dynamics by tuning the local environment rather than the material itself, yielding a new paradigm for nanoscale devices and energy conversion processes.
 A. Raja et al. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nature Communications 8, 15251 (2017)
[2[ A. Raja et al. Energy transfer from quantum dots to graphene and MoS2: the role of absorption and screening in two-dimensional materials. Nano Letters 16, 2328–2333 (2016)
 A. Raja et al. Enhancement of Exciton−Phonon Scattering from Monolayer to Bilayer WS2. Nano Letters 18, 6135-6143 (2018)
About the speaker
Archana Raja completed her PhD in Chemical Physics from Columbia University under the supervision of Profs. Tony Heinz and Louis Brus in 2016. After spending a year as a postdoc in the Applied Physics department at Stanford University, she joined the Kavli Energy and Nanoscience Institute at UC Berkeley as a Heising-Simons postdoctoral fellow, in the group of Prof. Paul Alivisatos.